The use of photostimulable phosphor image storage screens as a replacement for an x-ray film and other sensors is well known. Phosphor image screens work by trapping individual x-ray photons in a storage layer. The latent image trapped in the screen can then be read by scanning the storage layer using a suitable wavelength excitation beam, preferably from a focussed laser. The laser excitation beam causes the screen to release the latent image in the form of emitted stimulable phosphor light that is proportional to the x-ray energy applied to the screen during exposure. The emitted light is collected by an optical system and is converted into an electronic signal proportional to the emitted light. The electrical signal is then converted into a digital value and passed to a computer which generates and stores an image file. The image file can then be displayed as a representation of the original radiograph, with image enhancement software applied to augment the radiographic information.
Various known systems for moving a scanning head or directing a scanning beam across image or data storage screens are known. In one family of systems, an X-Y raster scan is taken as follows. The scanning head or beam first scans in a straight line across the screen in an X direction. The screen is then moved a short incremental distance in the Y direction. (Alternatively, the scanning head or the optics directing the beam can be moved incrementally in the Y direction). Thereafter, an X directional scan is repeated. Accordingly, by scanning back and forth in one direction, while intermittently advancing the screen (or re-directing the scanning beam), in a perpendicular direction, an X-Y raster scan is generated. In a second family of systems, the image or data storage screen is mounted to a rotating drum which is rotated about a center point in the plane of the screen while a scanning head is moved radially across the screen in a direction outwardly from the center point.
A problem common to both families of scanning systems is the problem of precisely controlling the movement of the scanning head, (or the movement of the optical system, such as a galvanometric mirror, directing the scanning beam). This is partially because the scanning head or scanning beam optics must be rapidly moved back and forth in at least one direction with the speed of such movement being constantly and quickly changing. Accordingly, scanning heads or scanning beam optical systems which rapidly move back and forth are typically subject to accelerations which cause problems including mechanical wear and failure and reduce read efficiency (ie: duty cycle) time to less than 100%. Accordingly, problems exist when attempting to accurately position such a moving scanning head or beam direction system to direct an incident beam at a desired location on the phosphor screen.
A second problem of existing systems is that such systems are configured such that the response radiation emitted by the screen is not directed back through the same optical train to a light detector, and as such a first optical train is required to direct and focus the incident light on the screen, and a second optical train is required to detect and measure the response radiation emitted by the screen.
It would instead be desirable to provide a system for high speed scanning of a phosphor screen, (or any other photostimulable media), which moves a scanning beam head in a path across the surface of the phosphor screen to generate a raster scan, yet avoids the problems of controlling the back and forth movement of the scanning head across the screen. It would also be desirable to avoid potential inaccuracies, control and wear and tear problems caused by acceleration forces moving such a scanning head back and forth in one or two directions, at the same time achieving 100% duty cycle read efficiency.
Moreover, it would be desirable to create a high speed scanning system which has minimal dead time during its operation such that a near continuous data stream can be generated as the phosphor screen is scanned.
Additionally, it would be desirable to create a high speed scanning system which does not require a transport mechanism which either moves the phosphor screen in two perpendicular directions (such as would be accomplished with an X-Y transport mechanism), or rotates the phosphor screen.
Additionally, it would be desirable to create a high speed scanning system which uses the same optical path for phosphor screen stimulation and data collection.